1. Field of the Invention
The present invention relates to an attachment member for an internal combustion engine that is attached to a screw attachment member. The screw attachment member is mounted on a flow pipe (an exhaust pipe) through which exhaust gas from an internal combustion engine flows.
2. Description of the Related Art
Known attachment members for attachment to a flow pipe of an internal combustion engine through which exhaust gas flows include a temperature sensor for detecting the temperature of the exhaust gas, a gas sensor for detecting the concentration of a specific gas composition in the exhaust gas, a particle sensor for detecting the particle mass in the exhaust gas, and a pressure sensor for detecting the pressure of the exhaust gas. The configuration of a temperature sensor described in Patent Literature 1 is conventionally known as one example of an attachment member for an internal combustion engine. A temperature sensor is attached to an exhaust pipe in a vehicle in order to detect the temperature of exhaust gas in the exhaust pipe while having a temperature sensing section such as a thermistor element and a Pt resistor element disposed in the exhaust pipe.
A boss including a ring seat face and a screw attachment member are mounted on an exterior wall of the exhaust pipe. Meanwhile, the temperature sensor includes a ring pressure section to be seated on the ring seat face and a fixing member (nut). The fixing member has a cylindrical shape and includes a threaded section on its outer periphery, the threaded section being screwable into the screw attachment member. While the threaded section of the fixing member is screwed (fastened) into the screw attachment member of the boss in a state in which the ring pressure section is seated on the ring seat face of the boss, a front-end facing surface of the fixing member is pressed against a rear-end facing surface of the ring pressure section. In this manner, the ring pressure section is fixed to the ring seat face to attach the temperature sensor to the boss (the exhaust pipe).
Thus, while the temperature sensor is attached to the exhaust pipe by a fastening axial force imparted by screwing the fixing member into an attaching member, the temperature sensor is exposed to the heat of exhaust gas once attached. When the temperature sensor is exposed to the heat of exhaust gas, the section of the boss of the exhaust pipe where the temperature sensor is attached, that is, the screw attachment member and the ring seat face, and the sections of the temperature sensor including the ring pressure section pressed against the ring seat face and the fixing member, may reach a high temperature such as 200 to 500° C., or 500° C. or higher depending on the circumstances. Therefore, when even one of the ring pressure section and the fixing member that constitute the temperature sensor and the boss that includes the screw attachment member is made from a material having a coefficient of thermal expansion largely different from that of the other members, the ring pressure section separates from the ring seat face of the boss based on the difference in coefficient of thermal expansion to possibly result in a loose screwing state. In order to solve this problem, in Patent Literature 1, the boss that includes the ring seat face, and the ring pressure section and the fixing member that constitute the temperature sensor are made to have approximately the same thermal deformation amount to prevent the screw from becoming loose.    [Patent Literature 1] JP-A-2002-122486
3. Problems to be Solved by the Invention
In the technique of Patent Literature 1, a restriction is placed on materials employed for forming not only the ring pressure section and the fixing member that constitute the temperature sensor, but also the boss that includes the screw attachment member and the ring seat face. Those materials should have approximately the same thermal deformation amount (e.g., be made of the same material). Thus, in attaching the temperature sensor to the exhaust pipe (boss), there is a drawback in that a realistic range in which the attachment member can be properly attached is extremely narrow. On the other hand, although lifting the restriction in selection of materials may increase flexibility in attaching the temperature sensor to the exhaust pipe, or expand the range of application of the temperature sensor to the exhaust pipe, eventually the above-described problem of the screw becoming loose must be taken into consideration.
In order to increase flexibility in attaching the temperature sensor to the flow pipe such as the exhaust pipe, or to expand the range of application of the temperature sensor to the flow pipe, one possible solution is to increase the fastening axial force itself. This is provided by screwing the fixing member into the flow pipe, so as to prevent the ring pressure section from separating from the ring seat face of the boss even when the temperature sensor is exposed to a high temperature. The screw is thereby prevented from becoming loose. However, because a friction coefficient by a contact surface (friction surface) between the fixing member and the ring pressure section is large, increasing the driving torque (tightening torque) of the fixing member in order to obtain a large fastening axial force is limited. In addition, when an excessive tightening torque is applied to the fixing member, the fixing member or the screw attachment member could be broken, so that it is not easy to increase the fastening axial force of the temperature sensor.
While the above problems are explained using a temperature sensor as an example, the same considerations may also arise among other attachment members for an internal combustion engine. These attachment members are configured such that while a threaded section provided to a fixing member is screwed into a screw attachment member of a boss of an exhaust pipe in a state where a ring pressure section is seated on a ring seat face of the boss, a top-end facing surface of the fixing member is pressed against a rear-end facing surface of the ring pressure section.